How can I send notifications to my team?

Every user can get two types of notifications -

In-app updates for tasks they follow, @mentions and comments to threads they're part of.
By default, everyone follows tasks that they create or that are assigned to them. You can also manually (un)follow tasks one by one form the task popup or in bulk by (un)following whole Projects and Teams.
Email notifications for tasks they follow, @mentions and comments to threads they're part of.

While users can choose to turn email notifications on/off from their profile settings, in-app notifications are delivered to everyone as long as they follow the task.

Since you don't know for sure if someone is following a task or not, the best way to make sure they react to your comments or changes is to use @mention to tag them in comments.